Timing of diapause in swallowtail butterflies

Prof. Wade Hazel and research students, summer 2010

Of the dozens of ongoing research projects at the park, Professor of Biology Wade N. Hazel's mesh bags generate some of the most curiosity. Hanging from trees along the trails, the bags are used to collect butterfly pupae. Understanding his research (photo gallery) requires a little bit of Butterfly 101.

It should come as no surprise that butterflies develop from caterpillars. After binging on the leaves of its favorite plant, a fat and happy caterpillar forms a chrysalis -- an elegant word for butterfly pupa -- to begin the metamorphosis into its adult, winged phase. A butterfly's life, from egg to adult, lasts only a few months, so many generations are born over the span of a single year.

But what happens in the winter, when temperatures are too cold for a butterfly to survive? The answer, says Hazel, is a clever feat of adaptation called diapause that allows butterflies to live through months of freezing weather.

"When they enter diapause, their metabolism slows, and they produce chemicals that prevent their tissues from freezing," Hazel says. "They may go into diapause in September and not come out until April or May."

Hazel and his students are trying to figure out if butterflies enter diapause based on the temperature in previous years -- in other words, whether butterflies have some sort of internal calendar, passed on through previous generations.

Access to the Nature Park is one of the reasons Hazel and his students are even able to do this research. All the local species of swallowtail butterflies that they work with are abundant in the park, including the giant swallowtail, the largest species of butterfly in North America.

"The Nature Park has the largest local density of giant swallowtails of any place I've seen in my life," Hazel says.